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The Solar System Interplanetary Matter, the Birth of the Planets And

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The Solar System Interplanetary Matter, the Birth of the Planets and Exoplanets Chapter 4 Reading assignment: Chapter 4 The structure of the Solar System Planets, satellites (moons), dwarf planets, asteroids, comets are part of the solar system The Asteroid belt, the Kuiper belt and the Oort cloud are also part of the structure of the solar system Kuiper belt • A region of the solar system located between 30-50 AU from the Sun • Bodies in the Kuiper belt are composed of “ices”, mainly methane, ammonia and water ices. • Pluto, Eris, Makemake and Haumea are examples of Kuiper belt objects The structure of the inner Solar System Ceres (Diameter ~ 940 km) and Vesta (Diameter ~ 500 km) are the largest bodies in the Asteroid belt. Ceres has been reclassified as a dwarf planet. The conditions established by the International Astronomical Union (IAU) to classify a body as a planet are: . It must clear its orbit of small bodies . It has a large mass that collapsed into a spherical shape Comets Astronomer Fred Whipple named them “Dirty snowballs” – they are composed of dust and rock in methane, ammonia and water ices The light we received from a comet comes from two sources: reflected light from the Sun and light emitted from the gas released by the comet, being ionized and excited by UV emission from the Sun. Parts of a comet: • Nucleus • Coma • Hydrogen envelope • Ion (or gas) and dust tails • The nucleus is the solid part of the comet. The size of the nucleus is just a few km in diameter. Its diameter too small to be resolved with telescopes; its is beyond the resolution of a telescope • The nucleus has been imaged by spacecraft only Halley’s Comet in 1986 •The coma can measure up to 100,000 km in diameter The highly eccentric elliptical orbits of most comet take them far beyond the orbit of Pluto • Long period comets take up to 1 million years to orbit the Sun! • These comets originate in the Oort cloud. The orientation of their orbits are random respect to the plane of the ecliptic • Short period comets orbit the Sun in 200 years or less (e.g. Halley’s comet, period ~ 76 years) • The orientation of their orbits are close to the ecliptic plane • Short period comets may have originated in the Kuiper belt • Kuiper belt comets get “kicked” into an eccentric orbit, bringing them into the inner part of the solar system The Oort cloud: a reservoir of millions or perhaps billions of comets and icy type of objects located at a distance of about 50,000 to 200,000 AU from the Sun The development of the gas and dust tails as the comet approaches the Sun When the comet begin approaching the Sun, the ices sublimate and release gas and dust from the nucleus . The dust forms the dust tail which point in the general direction of the trajectory of the comet. The gas points in direction opposite to the Sun and forms the gas or ion tail Comet Hale-Bopp (1997) dust and gas tails A recent comet: Comet McNaught 2007 Images of comet C/2012 S1 ISON It reached the closest distance from the Sun , about 1 solar diameter on November 28, 2013 (Thanksgiving day) An animation of comet ISON passing close to the Sun on Nov.- Dec. 2013 (Images SOHO Spacecraft). The nucleus did not survive the encounter. The intense heat of the Sun broke the nucleus in many small pieces. The pieces melted and the gasses sublimated. The nucleus of a comet The first image of the nucleus of comet Halley was obtained by the Giotto spacecraft in 1986 at a distance of about 400 km. Notice the jets coming out of the nucleus To the right, a diagram of Halley’s comet nucleus showing its size and structure Images of comet 67P (C-G) (Churyumov-Gerasimenko) taken by the Rosetta spacecraft in 2014-2015. The Rosetta spacecraft was the first spacecraft to enter orbit around a comet. It arrived on Sept. 10th 2014. Size of the comet are 4.1 x 4.3 km. Orbital period 6.44 years A comparison of the size of comet 67P (C-G) with downtown Los Angeles Recent images of comet 67P C-G taken by the Rosetta spacecraft in 2015 The spacecraft carried a lander. The lander crash-landed on the surface of the comet on Sept. 30, 2016 Details of the surface Image taken from a An outburst of activity showing “Sinkholes”. distance of 150 km “Sinkholes” form from showing the jets the collapse of material after ices sublimated Meteoroid, Meteor and Meteorite Castor and Pollux (The Twins, Meteoroid – interplanetary rocky material smaller Gemini than 100m (down to grain size). constellation) •It is called a meteor when it enter and burns in the Meteor Earth’s atmosphere radiant (Geminids •If some material survives the entry and makes it to meteor the ground, it is called a meteorite shower) Meteor showers Most meteor showers are the result of the Earth passing through the orbit of a comet which has left debris along its path. They take the name of the constellation were the radiant seems to be located Some 2020 Meteor showers: Perseids ( 109P/Swift-Tuttle) - August 12-13 about 90/hour Orionids (Halley’s comet) – Oct 21-22 (after midnight in the Eastern sky, only 20/hour) Leonids (Comet Tempel_Tuttle) – Nov 17-18 (after midnight in the Eastern sky, only 20/hour) Geminids (Phaethon object) – December 13-14 Probably one of the best for 2020, predicted about 120 meteor/hour). The Moon phase will be New Moon. Good for observing the meteor shower. Types of meteorites Stony. This are the most common meteorites Iron-Nickel. Easy to find using metal detectors An iron-nickel meteorite is a fragment of a larger body. The body was large enough to generate internal heat and went through the differentiation process. Heavier material (iron, nickel) sunk to the core. Collisions broke the large body, exposed the central part (core) from which the smaller pieces came from. Stony-Iron A stony meteorite Usually covered by a dark crust, created by the melting of the surface during the entry through the atmosphere A iron-nickel meteorite The Windmanstatten pattern in the etched slice of an iron-nickel meteorite An example of slice of a pallasite meteorite (olivine crystals) Some meteorites can be large The “Hoba” iron-nickel meteorite, in Namibia, Africa. Estimated mass about 60 tons. Composition, 80% Fe and 16% Ni Known meteorite impact craters sites Meteoroids Most meteoroids are rocky,. A small fraction are mainly iron and nickel Some contain carbonaceous material - rich in organic material (amino acids). This organic material is formed in interstellar space Meteoroids are old - 4.5 billion years based on carbon dating. Most were formed when the solar system formed •The Barringer Crater. Usually known as the “meteor” crater near Winslow, AZ • One of the best preserved craters • Formed from the impact of a 50 m body weighing 200,000 tons! • Diameter of crater 1.2 km • Ratio size crater/size impacting body = 24 •Age, around 25,000 years Asteroids - rocks with sizes greater than 100m across •Most asteroids are in orbit around the Sun in what it is called the Asteroid belt between the orbits of Mars and Jupiter • About 2000 asteroids have orbits that cross Earth’s path. Called NEO, Near Earth Objects. • Some of these may come at distances < 0.05 AU from the Earth. The are called PHA’s (Potentially Hazardous Asteroids) Some of the more recent collisions • Extinction of the Dinosaurs A 10-15 km size asteroid that collided about 65 millions years ago in Chicxulub, in the Yucatan peninsula (Mexico). It left a crater about 180 Km diameter A layer of clay enriched in iridium found in many part of the world fits the age of the impact. A cloud of dust rich in iridium circled the Earth. Iridium is found in meteorites and asteroids The cloud of dust and the smoke of fires generated by the impact may have shrouded the planet for a few years, extinguishing the Sun’s rays, killing plants and disrupting the food chain • The Tunguska event in 1908 in Siberia is one of the most recent. The body (30m size) exploded several km above the surface. It did not create a crater, just a depression. • The most recent: The Chelyabink event. Fell in Russia on February 15, 2013. The size was about 17-20 m. It exploded at an altitude of several kilometers and generated a shock wave that broke windows and took down part of a building wall. A few pieces were recovered. Check the spaceweather.com website for a list of asteroids (called PHAs) coming close to the Earth! Asteroids range in size from 100m to ~1000km They are composed of carbon, iron and other rocky material. The Asteroid belt is a group of asteriods that appear to have never joined to make a planet (as opposed to having once been a planet that was later destroyed). Some of the evidence is this: •The total mass of all the asteroids is too small to be a planet •They have different chemical compositions The reason for the asteroid belt is the presence of Jupiter... Jupiter may have prevented the formation of a body at the distance from the Sun where the Asteroid belt is located. The orbital period of those small bodies may have a resonance with the orbital period of Jupiter. There are gaps in the asteroid belt at several distances from the Sun where the orbital period is a fraction of Jupiter orbital period (1/3, 2/5, 1/2…) Images of asteroids (All the images were taken by spacecrafts) More images of several asteroids taken by spacecrafts The image of Vesta (Diameter 525 km, second largest asteroid) was taken by the Dawn spacecraft mission in 2011.
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